Coriolis mass flow meter

Abstract

The invention provides a Coriolis mass flow meter which comprises a corrosive fluid as a measurement object and does not have the risk of metal ion elution. The present invention is provided with: a straight pipe-type pipe (1) through which a measurement fluid flows; an exciter (2) that excites the piping (1); a first vibration detector (3) and a second vibration detector (4) that detect the vibration state of the pipe (1); and supports (8a, 8b) that support both ends of the pipe (1) so as to become fixed ends with respect to vibration, the exciter (2), the first vibration detector (3), and the second vibration detector (4) are supported by the frames (9a, 9b), the frames (9a, 9b) are connected to the supports (8a, 8b), and the supports (8a, 8b) are connected to the supports (8a, 8b). The mass flow rate of the fluid flowing through the piping is determined on the basis of the phase deviation of the vibration waveforms detected by the first vibration detector (3) and the second vibration detector (4). The piping (1), the support bodies (8a, 8b), and the frames (9a, 9b) are formed from a highly elastic plastic material.

Description

Technical Field

[0001] The present invention relates to a Coriolis mass flowmeter for detecting torsional vibration using the action of the Coriolis force generated by a fluid in a vibrating flow path, thereby measuring the mass flow rate of the fluid. Background Art

[0002] In the past, a Coriolis mass flowmeter was used as a direct measurement unit for mass flow. This is a flowmeter that utilizes the following situation: when the fluid flowing in the pipe rotates, it is subjected to a Coriolis force proportional to the vector product of the flow vector and the angular velocity vector of the rotation, and this Coriolis force is proportional to the mass flow rate. The following method is usually used: the pipe is vibrated to detect the elastic deformation of the pipe caused by the Coriolis force of the internal fluid.

[0003] The Coriolis mass flowmeter uses an exciter to forcibly vibrate the piping through which the fluid to be measured passes, detects the phase difference of the vibration generated on the upstream and downstream sides of the flow path according to the mass flow rate of the fluid, and calculates the mass flow rate based on the phase difference. In order to generate vibration efficiently, the Coriolis mass flowmeter usually excites the natural vibration frequency of the piping through which the fluid passes. The main factors that determine the natural vibration frequency of the piping are the elastic modulus (longitudinal elastic coefficient) of the piping material and the shape of the piping. For metal piping, the elastic modulus is relatively stable with respect to temperature changes, and the shape is unlikely to change over time, so it is often used as the piping of the Coriolis mass flowmeter.

[0004] As such a prior art, the following is known: when a fluid corrosive to metal is to be measured, a Coriolis mass flow meter which is good at measuring corrosive fluids is used, such as Figure 2 As shown in (a), the U-shaped composite curved conduit 21 excited at the natural vibration frequency is fixed to the support member 23 through the fixing portion 22, as shown in FIG. Figure 2 As shown in (b), the outer side of the double-structured U-shaped composite curved conduit 21 is made of Elinval nickel-chromium alloy 24, and the inner side 25 is coated with fluororesin (Patent Document 1). However, since the Coriolis mass flowmeter is composed of a U-shaped conduit, it is difficult to apply fluororesin to the curved portion.

[0005] In addition, it is difficult to make a thick film of fluororesin coating, and if the coating is not reliably implemented, there is a concern that metal ions will be eluted into the fluid, so there is a demand not to use metal as a piping material. Figure 3 As shown in FIG. 2 , a Coriolis mass flowmeter in which a pipe is formed of perfluoroalkoxyalkane (PFA) is proposed (Patent Document 2). Figure 3In the figure, the fluid of the processing material is received from the supply pipe 31, and the fluid is supplied to the piping 33 through the processing connection part 32. The piping 33 is excited by the exciter 34 at a frequency that resonates with the flow of the fluid. The fluid passes from the piping 33 through the processing connection part 35, the tube 36 that changes the flow direction of the fluid, the processing connection part 37, the return piping 38, and the processing connection part 39 to reach the outlet piping 40. Here, the piping 33 and the return piping 38 are made of PFA. However, in the case where the piping is composed only of fluororesin, changes in elastic modulus caused by temperature and creep due to aging may occur. The Coriolis mass flowmeter vibrates the piping for measurement in principle, but since the change in elastic modulus affects its vibration, it is difficult to accurately measure the mass flow rate.

[0006] In addition, if Figure 4 As shown in the patent document 3, a Coriolis mass flowmeter having a subassembly structure formed of an elastic polymer material is proposed, wherein the Coriolis mass flowmeter has two flow detection components each having one or more linear portions and integrally connected to a base. Figure 4 In the solid subassembly 51 formed of a polymer material CNC-processed from a block of elastic polymer material, flow paths 52 and 53 are formed completely from end to end in the lateral direction along the center line of U, and flow paths 54, 55, 56, 57 are formed to completely penetrate the support portion 58 along the center line of U. And, as Figure 5 , Figure 6 As shown in the patent document 4, a Coriolis mass flowmeter is proposed, which comprises a main body 61 made of the same polymer material, at least four tubular port extensions 62A, 62B, 62C, 62D which are integrated with the main body 61 and each include a welding surface, a manifold flow passage 63A, 63B, 63C, 63D, an insulating plate 64A, 64B, 64C, 64D which are integrated with the main body 61 and the at least four tubular port extensions, and two flow sensing components 65A, 65B including two open ends (Patent Document 4). In addition, as Figure 7 As shown, a Coriolis mass flowmeter is proposed, which includes flow sensing components 71A, 71B and a dynamically responsive support body 72 for holding the flow sensing components 71A, 71B, the flow sensing components are fluorine-based resins such as PFA, polyetheretherketone (PEEK), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE), and the thermal expansion coefficient of the support body material is roughly close to that of the fluorine-based resin, or smaller than that of the fluorine-based resin (Patent Document 5).

[0007] However, the Coriolis mass flowmeters disclosed in Patent Documents 3 to 5 cannot cope with changes in elastic modulus caused by temperature. That is, the spring constant of the piping material (proportional to the Young's modulus) changes according to the temperature, which directly affects the accuracy of the Coriolis mass flowmeter. The temperature of the flow detection element also changes according to the temperature of the fluid and / or the surroundings, so in order to maintain the accuracy of flow measurement in the Coriolis mass flowmeter, temperature compensation is required. Regarding the data of Young's modulus to temperature, data of almost all metal alloys (stainless steel or titanium, etc.) used in the manufacture of Coriolis mass flowmeters in the prior art can be obtained from NIST (or other technical data). However, for elastic polymers, matching data (elastic modulus to temperature, etc.) are usually not available, or only a few temperatures are recorded in publications. Therefore, although the prior art that records the use of plastics in the manufacture of Coriolis mass flowmeters also mentions means for detecting the temperature of flow detection elements, it does not record how to achieve effective temperature compensation for specific elastic polymer materials within a certain range of operating temperatures. Importantly, without such temperature compensation, the flow meter cannot be used in applications where the temperature of the sensor is substantially different from the temperature at which it was calibrated.

[0008] Furthermore, when the purpose is to apply to a fluid with a very small flow rate, in order to realize a highly sensitive Coriolis mass flowmeter, it is necessary to increase the distance between the two vibration detectors as much as possible and to reduce the torsion spring constant of the pipe to facilitate torsion.

[0009] For example, in Patent Document 6, Figure 8 As shown in the figure, a Coriolis mass flowmeter is proposed, which has a pipe for fluid flow consisting of an inner tube 82 connected to a flow path 81 and an outer tube 83 stacked on the outer peripheral surface of the inner tube 82. Here, the inner tube 82 is a fluorine-based resin, and the outer tube 83 is formed by winding a prepreg in which glass fibers are arranged in an uncured epoxy resin around the outer periphery of the inner tube 82 and curing it. The elastic modulus is larger than that of the inner tube 82. The outer tube 83 has fibers F1 and F2 arranged on the outer peripheral surface 84 of the inner tube 82 and a resin 85 for forming the fibers F1 and F2 to be fixed or pressed to the inner tube 82. In addition, in Patent Document 7, as Fig. 9 As shown, a Coriolis mass flowmeter is proposed, which has a frame composed of a main frame 91 and a sub-frame 92, a housing 93, and a vibration tube 94. The metering part of the vibration tube 94 is set to a fluororesin reinforced with carbon fiber, and the inlet part and the outlet part of the supply and discharge part of the vibration tube that receives and discharges the fluid are set to a fluororesin that is not reinforced with fibers.

[0010] First, in order for the Coriolis mass flowmeter to measure the mass flow rate of a fluid with a very small flow rate with high accuracy, as described above, it is necessary to increase the distance (d) between the two vibration detectors as much as possible and reduce the torsional spring constant (Kθ) of the pipe.

[0011] However, in the case of a conventional U-shaped piping, by increasing the above-mentioned interval d, the moment of inertia in the torsion direction becomes larger, and at the same time, the torsion spring constant Kθ becomes larger, and the vibration frequency of the torsion (Coriolis vibration frequency) becomes smaller. If the Coriolis vibration frequency becomes smaller, it is easily affected by vibration noise from the outside. In addition, if the above-mentioned interval d is increased, the pressure loss of the fluid becomes larger, not only is it limited by the maximum flow rate, but the fluid inside the piping is not completely discharged and remains attached. Therefore, in manufacturing processes such as semiconductor manufacturing processes and pharmaceutical manufacturing processes that require extremely high cleanliness of manufacturing equipment, it is difficult to completely clean the inside of the piping even if fixed cleaning and fixed sterilization are implemented.

[0012] In order to minimize the torsion spring constant Kθ of the piping, it is required to minimize the bending rigidity EI (E: elastic modulus, I: section inertia moment). This means making the piping as thin as possible and reducing the wall thickness. This is in line with the purpose of measuring a small flow rate of fluid, but if the piping is made thinner, the pressure loss will increase.

[0013] As a result, in a double structure in which the outer tube covering the outer peripheral surface of the inner tube is made of a fiber-reinforced resin with a large elastic modulus (Patent Document 6), even if the inner diameter of the piping is reduced, the wall thickness becomes thicker, so there is a limitation in reducing the torsion spring constant Kθ, and there is a limit to improving the sensitivity in order to measure the fluid with a small flow rate with high precision.

[0014] In the Coriolis mass flowmeters of Patent Documents 2 and 5, the piping is formed of fluororesin, but its density is lower than that of metal, so if it is of the same size, the mass of the piping portion is smaller than that of the metal. Since a pair of coils and magnets are mostly used in the exciter and two vibration detectors loaded on the piping, the relatively heavy mass is concentrated on the elastic polymer such as fluororesin. In this way, if concentrated mass is added to the piping, it will affect the density measurement of the fluid, reduce sensitivity, and reduce accuracy. In paragraph 0029 of Patent Document 5, it is recorded that "other types of motion sensors such as optical sensors can also be used", but it only describes other methods of motion sensors and does not mention the impact of the concentrated mass added to the piping on the density measurement of the fluid.

[0015] In addition, the purpose of Patent Document 8 is to provide a Coriolis mass flowmeter of two parallel arch tubes, which has less interference vibration, installation conditions, piping stress and thermal influence, such as Fig.10As shown, a Coriolis mass flowmeter is proposed, which comprises: two flow tubes 101, 102 bent into an arch; an inlet side manifold and an outlet side manifold 103 at both ends of the flow tubes connected by welding; a driving device 104, which causes one flow tube to resonate and drive with phases opposite to each other relative to the other flow tube; and a pair of vibration detection sensors 105, 106, which are arranged at symmetrical positions on the left and right sides relative to the installation position of the driving device 104, and detect a phase difference proportional to the Coriolis force.

[0016] However, including Patent Document 8, Patent Documents 1 to 7 do not mention the measurement of fluid density.

[0017] In addition, Patent Document 9 discloses a double straight tube Coriolis flowmeter. Fig.11 As shown, the double straight tube Coriolis flowmeter has a hollow cylindrical housing 112 with connecting flanges 111 at both ends, a straight tube flow tube 113 for the measured fluid to flow is coaxially arranged inside the housing 112, and a hollow cylindrical outer tube 115 is concentrically fixed on both sides of the flow tube 113 via a connecting plate 114 in a manner of forming a concentric double tube, and a balancing weight 116 is installed in the center of the outer tube 115, and a driving device 117 is installed on the outer tube 115, so that the flow tube 113 vibrates in the primary mode of its natural vibration. When the fluid flows, the Coriolis forces on the inlet and outlet sides are in opposite directions with the central part where the vibration speed is the largest as the boundary, and the flow tube 113 bends in an undulating manner, which is called a secondary mode component. The flow tube 113 is displaced in the form of a superposition of a primary mode vibration based on the excitation generated by the driving device and a secondary mode vibration based on the Coriolis force. A pair of sensors 118 are arranged on the outer tube 115 at the position where the secondary mode component is the largest on both sides of the driving device 117 to detect the phase difference of the flow tube 113 caused by the Coriolis force, thereby being able to obtain the mass flow rate.

[0018] However, in the double straight tube Coriolis flowmeter disclosed in Patent Document 9, when the temperature change of the measured fluid occurs and a very large temperature difference occurs between the flow tube and the outer tube, stress is generated in the longitudinal direction, and the natural vibration frequency of the tube changes due to the change in spring constant caused by the generation of thermal stress. As a result, there is a disadvantage that the energy balance is destroyed and resonance driving is difficult.

[0019] Prior art literature

[0020] Patent Literature

[0021] Patent Document 1: Japanese Utility Model Publication No. 64-15921

[0022] Patent Document 2: Japanese Patent Application No. 2005-510703

[0023] Patent Document 3: Japanese Patent No. 5602884

[0024] Patent Document 4: Japanese Patent No. 6257772

[0025] Patent Document 5: Japanese Patent No. 6581309

[0026] Patent Document 6: Japanese Patent No. 5086814

[0027] Patent Document 7: Japanese Patent No. 5582737

[0028] Patent Document 8: Japanese Patent No. 3656947

[0029] Patent Document 9: U.S. Patent No. 6,336,369 Summary of the invention

[0030] 1. Technical issues to be resolved

[0031] The present invention is completed in view of such problems in the prior art, and its purpose is to provide a Coriolis mass flowmeter, which includes corrosive fluids as measurement objects and does not have the risk of metal ion dissolution. In addition, the present invention aims to provide a Coriolis mass flowmeter that can achieve a thinner diameter of the piping and can stably measure relative to temperature changes. A further object of the present invention is to provide a Coriolis mass flowmeter that is less affected by external vibrations and can measure low-density fluids with high sensitivity. A further object of the present invention is to provide a Coriolis mass flowmeter that can measure the mass flow rate and density of fluids with tiny flow rates with high sensitivity even if it is miniaturized. A further object of the present invention is to provide a Coriolis mass flowmeter that is less affected by vibration noise and viscosity.

[0032] (II) Technical solution

[0033] The present inventors have conducted intensive studies to solve the above-mentioned technical problems, and have adopted the following means.

[0034] (1) The first invention is a Coriolis mass flowmeter, characterized in that it comprises: a straight tube type piping for measuring fluid flow; an exciter for exciting the piping; a first vibration detector and a second vibration detector for detecting the vibration state of the piping; and a support body for supporting two ends of the piping so that the two ends of the piping become fixed ends relative to the vibration, the exciter, the first vibration detector and the second vibration detector are supported by a frame, the frame is connected to the support body, the mass flow rate of the fluid flowing in the piping is calculated based on the phase deviation of the vibration waveform detected by the first vibration detector and the second vibration detector, and the piping, the support body and the frame are formed of a high elastic plastic material.

[0035] (2) A second invention is the Coriolis mass flowmeter as described in (1) above, wherein the high elastic plastic material is carbon fiber reinforced thermoplastic (CFRTP).

[0036] (3) A third invention is the Coriolis mass flowmeter according to (2) above, wherein the thermoplastic plastic is a fluororesin.

[0037] (4) The fourth invention is a flow measurement device described in any one of (1) to (3) above, characterized in that, when the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, and the mass of the exciter is set to m3, m3 is greater than the sum of m1 and m2.

[0038] (5) The fifth invention is a Coriolis mass flowmeter described in any one of (1) to (3) above, characterized in that, when the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, the mass of the exciter is set to m3, the total of m1, m2 and m3 is set to m, the mass of the piping is set to Mt, the mass of the fluid in the piping is set to Mf, and M=Mt+m+Mf, m=0.4M or less.

[0039] (6) The sixth invention is a Coriolis mass flowmeter as described in any one of (1) to (3) above, characterized in that the first vibration detector and the second vibration detector are acceleration sensors located at symmetrical positions around the exciter.

[0040] (7) The seventh invention is a Coriolis mass flowmeter as described in any one of (1) to (3) above, characterized in that the first vibration detector and the second vibration detector are acoustic sensors located at symmetrical positions around the exciter.

[0041] (8) An eighth invention is the Coriolis mass flowmeter according to any one of (1) to (3) above, wherein the exciter is a piezoelectric element.

[0042] (9) The ninth invention is a Coriolis mass flowmeter, characterized in that it comprises: a straight pipe type piping for a flow of a measuring fluid; a vibrator for vibrating the piping; a first vibration detector and a second vibration detector for detecting a vibration state of the piping; and a left support and a right support for supporting two ends of the piping so that the two ends of the piping become fixed ends relative to the vibration, the vibrator, the first vibration detector and the second vibration detector being supported by a frame, the frame being at least one of a first frame and a second frame connected to the support, based on the first vibration detector and the second vibration detector. The mass flow rate of the fluid flowing in the piping is calculated from the phase deviation of the vibration waveform detected by the vibrator. The piping is formed by a straight pipe, and the first frame and the second frame are located at symmetrical positions with respect to the central axis of the length direction of the piping. The vibrator is located in the center of the first frame equidistant from the support body on the left and the support body on the right. The first vibration detector and the second vibration detector are located on the first frame at symmetrical positions centered on the vibrator, and the first vibration detector and the second vibration detector are also supported on the second frame in a symmetrical position relative to the first vibration detector and the second vibration detector supported on the first frame across the central axis of the length direction of the piping.

[0043] (10) The tenth invention is a Coriolis mass flowmeter as described in (9) above, characterized in that it has a differential circuit for obtaining the difference of the output of the first vibration detector and a differential circuit for obtaining the difference of the output of the second vibration detector, and removes the in-phase signal by measuring the phase difference between the outputs of the above two differential circuits.

[0044] (11) An eleventh invention is the Coriolis mass flowmeter according to the above (10), wherein the first vibration detector and the second vibration detector are electrostatic capacitance sensors, and a metal thin film is attached to the pipe.

[0045] (12) The twelfth invention is a Coriolis mass flowmeter as described in any one of (9) to (11) above, characterized in that the first vibration detector and the second vibration detector are optical displacement sensors and a metal film is attached to the piping.

[0046] (13) The thirteenth invention is a Coriolis mass flowmeter as described in any one of (9) to (11) above, characterized in that the exciter is composed of a magnetic body such as a permanent magnet and an electromagnetic drive coil corresponding to the magnetic body, the magnetic body is an exciter supported on the piping and excites the piping, and a non-magnetic body of the same shape and mass as the magnetic body is supported on the piping in a manner that is symmetrical to the magnetic body relative to the longitudinal center axis of the piping.

[0047] (14) The fourteenth invention is a Coriolis mass flowmeter as described in (13) above, characterized in that, when the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, and the mass of the exciter is set to m3, m3 is greater than the sum of m1 and m2, the mass of the first vibration detector supported on the first frame and the mass of the first vibration detector supported on the second frame are both m1 / 2, the mass of the second vibration detector supported on the first frame and the mass of the second vibration detector supported on the second frame are both m2 / 2, and the mass of the magnetic body and the non-magnetic body are both m3 / 2.

[0048] (III) Beneficial effects

[0049] If the carbon fiber reinforced thermoplastic plastic forming the piping, support body and frame is a carbon fiber reinforced fluororesin, its bending elastic modulus is about 32GPa, which is about 17% of the longitudinal elastic modulus of stainless steel (SUS304) 193GPa. In addition, the linear expansion coefficient of carbon fiber reinforced fluororesin (10 -6 / ℃) is close to zero, while the linear expansion coefficient of stainless steel (SUS304) (10 -6 / °C) is 16. Therefore, if the pipes, supports, and frames are formed using carbon fiber reinforced fluororesin, the dimensions are less likely to change due to temperature and chemical resistance can be achieved.

[0050] The density of the fluid is measured by measuring the change in the Coriolis vibration frequency corresponding to the change in the fluid density. Regarding the slope of the change in the Coriolis vibration frequency, if the mass of the vibration detector that detects the vibration is larger than the mass of the pipe to a certain extent, the above slope becomes gentle, and the change in the Coriolis vibration frequency becomes smaller relative to the change in the fluid density, which reduces the detection sensitivity. Therefore, when the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, and the mass of the exciter is set to m3, m3 is greater than the sum of m1 and m2, and when the sum of m1, m2 and m3 is set to m, the mass of the pipe is set to Mt, the mass of the fluid in the pipe is set to Mf, and M=Mt+m+Mf, m=0.4M or less, thereby improving the detection sensitivity of the fluid density. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 FIG. 1 is a schematic structural diagram of a first embodiment of a Coriolis mass flowmeter of the present invention including related equipment.

[0052] Figure 2 (a) is a schematic structural diagram of a Coriolis mass flowmeter of Patent Document 1. Figure 2 (b) is an enlarged cross-sectional view of the fixed portion.

[0053] Figure 3 This is a top view of the Coriolis mass flowmeter of Patent Document 2.

[0054] Figure 4 This is a diagram showing a schematic structure of a Coriolis mass flowmeter disclosed in Patent Document 3.

[0055] Figure 5 This is a diagram showing a schematic structure of a main body, a tubular port extension, a manifold flow passage, and an insulating plate of the Coriolis mass flowmeter of Patent Document 4.

[0056] Figure 6 This is a diagram showing a schematic structure of a flow sensing component of the Coriolis mass flowmeter of Patent Document 4.

[0057] Figure 7 This is a diagram showing a schematic structure of a Coriolis mass flowmeter disclosed in Patent Document 5.

[0058] Figure 8 This is an enlarged cross-sectional view of the piping of the Coriolis mass flowmeter of Patent Document 6.

[0059] Fig. 9 This is a diagram showing a schematic structure of a Coriolis mass flowmeter of Patent Document 7.

[0060] Fig.10 This is a diagram showing a partial cross section of the Coriolis mass flowmeter of Patent Document 8 and a side view cut at a manifold portion.

[0061] Fig.11 This is a schematic diagram showing a double straight tube Coriolis flowmeter of Patent Document 9.

[0062] Fig.12 (a) and (b) are diagrams showing the working principle of a straight tube Coriolis mass flowmeter. Fig.12 (a) shows a state where the pipe is filled with fluid and the pipe is vibrated by an exciter at a flow velocity v=0. Fig.12 (b) shows a state in which torsional vibration occurs in the pipe when the fluid flows in the pipe at a flow velocity v (≠0). Fig.12 (c) is shown in Fig.12 In the case of (b), a diagram is a diagram of sinusoidal waveforms detected by a first vibration detector and a second vibration detector that are arranged at symmetrical positions with respect to the vibration exciter.

[0063] Fig.13The horizontal axis is the ratio of the additional mass m (m1+m2+m3) to the total mass M (Mt+m+Mf) of the pipe when the pipe material is CFRTP (symbol "●"), SUS316 (symbol "▲") or PFA (symbol "■"), and the frequency density margin (Hz / (g / cm 3 )) is the graph with the vertical axis, which shows the case where m3=m1+m2.

[0064] Fig.14 The horizontal axis is the ratio of the additional mass m (m1+m2+m3) to the mass M (Mt+m+Mf) of the entire pipe when the pipe material is CFRTP, and the frequency density margin (Hz / (g / cm 3 )) is the graph with the vertical axis. When the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, and the mass of the exciter is set to m3, the symbols "■", "▲", and "●" respectively represent the cases where the ratio of m3 / (m1+m2) is 3 / 1, 2 / 1, and 1 / 1.

[0065] Fig.15 FIG. 1 is a schematic structural diagram of a second embodiment of the Coriolis mass flowmeter of the present invention including related equipment.

[0066] Fig.16 FIG. 1 is a schematic structural diagram of a third embodiment of the Coriolis mass flowmeter of the present invention including related equipment.

[0067] Fig.17 FIG. 1 is a schematic structural diagram of a fourth embodiment of the Coriolis mass flowmeter of the present invention including related equipment.

[0068] Fig.18 FIG. 1 is a schematic structural diagram of a fifth embodiment of the Coriolis mass flowmeter of the present invention including related equipment. DETAILED DESCRIPTION

[0069] Hereinafter, specific embodiments of the present invention will be described, but the present invention is not limited to the following embodiments, and various changes and modifications can be made without departing from the technical scope of the present invention.

[0070] There are many kinds of fluororesins, and as the fluororesin used in the present invention, a fluororesin that can be melt-molded is preferred. For example, perfluoroalkoxyalkane (PFA), perfluoroethylene propylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), etc. can be used.

[0071] As the carbon fibers used in the present invention, there are, for example, PAN based on polyacrylonitrile fibers, asphalt based on coal tar and petroleum asphalt (isotropic and mesophase based on the internal structure), cellulose based on viscose fibers, cellulose acetate and the like, vapor phase growth based on hydrocarbons and the like. In addition, graphite fibers of these carbon fibers may also be used. In addition, metal-coated carbon fibers may be formed by coating these carbon fibers with at least one layer of metals such as nickel, ytterbium, gold, silver, and copper by plating (electroplated, chemically plated), CVD, PVD, ion plating, and vapor deposition. In addition, two or more of them may be mixed to form a carbon fiber.

[0072] The pipe, support and frame of the present invention are preferably made of carbon fiber reinforced fluororesin, but may contain additives other than fluororesin and carbon fiber within the scope of not hindering the effect of the present invention. As such additives, flame retardants, conductive imparting agents, crystal nucleating agents, ultraviolet absorbers, antioxidants, vibration damping agents, antibacterial agents, insect repellents, deodorants, anti-coloring agents, heat stabilizers, mold release agents, antistatic agents, plasticizers, lubricants, colorants, pigments, dyes, foaming agents, foam suppressants, coupling agents, etc., may be cited. Two or more of these may be used.

[0073] The pipe, support body and frame of the present invention are preferably formed by injection molding. Injection molding has high productivity and can achieve low cost because it can perform molding cycles and mold complex shapes.

[0074] When the piping, support body and frame of the present invention are made by injection molding, it is preferably carried out under the following conditions. The screw is usually composed of a supply part, a compression part and a metering part. It is preferably a full-thread shape that minimizes the degree of kneading. It can also be used by adjusting the level of kneading by adding a part of the kneading part. By using a screw with a kneading part as small as possible for molding, fiber breakage can be suppressed. In addition, the gap between the cylinder and the screw also has a great influence on the fiber length. By increasing the gap, the kneading can be reduced and the fiber breakage can be suppressed. In addition, the size of the nozzle diameter also affects the fiber length. If the nozzle diameter is small, high shear is applied when the molten molding material passes through, resulting in fiber breakage. The fiber length can also be extended by increasing the nozzle diameter. In addition, shear can also be suppressed by increasing the flow channel of the mold, which can extend the fiber length. Furthermore, by setting it as a hot runner or adjusting the temperature of the mold appropriately, the viscosity of the flowing resin can be reduced and the fiber breakage can be suppressed.

[0075] Regarding the molding conditions, it is preferred to set the cylinder temperature to a high temperature within the range where the matrix resin does not decompose, reduce the screw speed, shorten the metering time, and set the back pressure to a low level. By increasing the cylinder temperature, the viscosity of the molten resin is reduced, the shear force applied to the fiber becomes smaller, and breakage can be suppressed. In addition, if the screw speed is reduced, the metering time is shortened, and the back pressure is set to a low level, the mixing and shearing can be minimized for molding, and a molded product with a long fiber length can be obtained, which becomes a molded product with low anisotropy and high strength. The reason why the strength anisotropy of the molded product is reduced is that if the fiber length is relatively long (more than 1 mm) to a certain extent, the fibers inside the molded product resist the flow of the resin and are oriented in the vertical direction. On the surface of the molded product that is instantly cooled and solidified by the mold, the fibers are oriented in the direction of the resin flow. As a result, the fibers are not in a form that is reinforced in one direction, but in a form that is reinforced in all directions, and the anisotropy of the molded product is reduced.

[0076] The volume content of the carbon fibers in the carbon fiber reinforced thermoplastic of the present invention is preferably 20 to 40%, more preferably 25 to 35%.

[0077] Example

[0078] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to these examples, and various changes and modifications can be made without departing from the technical scope of the present invention.

[0079] A twin-screw extruder manufactured by Shibaura Machine Co., Ltd. (screw diameter 30 mm, die diameter 5 mm, barrel temperature 280°C, rotation speed 150 rpm) was used to cut a continuous carbon fiber bundle manufactured by Mitsubishi Chemical Corporation into 6 mm long short strands, which were fully dried to a moisture content of 0.05% or less and then fed from a side hopper. In addition, a fully fluorinated high-flowability fluororesin "PFA AP-201SH" manufactured by Daikin Industries was fed from a main hopper as a thermoplastic resin, and gut (Japanese: ガット) containing discontinuous carbon fibers was continuously extruded while they were fully kneaded. After cooling, the gut was cut into 5 mm long strands using a cutter to obtain a carbon short fiber forming material.

[0080] The molding material was dried in a vacuum at 80°C for more than 5 hours and then molded using a hydraulic horizontal injection molding machine with a full-screw screw. Figure 1 A molded product of the shape shown.

[0081] exist Figure 1In the figure, 1 is a straight pipe type piping for measuring the flow of fluid from 10 to 11, and a vibration plate (not shown) is provided in the flow path inside the piping 1 along the flow direction, and two points of the flow direction of the vibration plate are supported on the inner wall of the piping 1 by two supporting members (not shown). A magnetic body such as a permanent magnet (not shown) is fixed to the vibration plate, and an exciter 2 is arranged at a position opposite to the magnetic body, and a first vibration detector 3 and a second vibration detector 4 are arranged at equal distances from the respective positions of the two supporting members, and the first vibration detector 3 and the second vibration detector 4 are located at symmetrical positions with the exciter 2 as the center.

[0082] The two support members are provided at positions corresponding to the nodes of the primary natural vibration mode when the vibration plate is placed in a completely free state.

[0083] In addition, the exciter 2 is excited by the excitation circuit 5, and the output signals of the first vibration detector 3 and the second vibration detector 4 are input to the phase difference measuring device 6. The excitation circuit 5 excites at a period of the primary bending natural vibration frequency of the vibration plate in the state where the pipe 1 is filled with fluid. The vibration of the vibration plate is measured as a vibration displacement or a vibration waveform by the first vibration detector 3 and the second vibration detector 4. The phase difference measuring device 6 feeds back the metering signal obtained by the first vibration detector 3 and the second vibration detector 4 to the excitation circuit 5, and changes the excitation frequency in such a way that the output signals of the first vibration detector 3 and the second vibration detector 4 are always the maximum. In addition, the phase difference measuring device 6 measures the phase difference between the output signals of the first vibration detector 3 and the second vibration detector 4, and outputs the measurement result to the calculation circuit 7. The calculation circuit 7 can calculate the mass flow rate of the measured fluid based on the measurement result of the phase difference measuring device 6.

[0084] In addition, there are a left support body 8a and a right support body 8b that support both ends of the piping 1 as fixed ends relative to vibration, and the above-mentioned exciter 2, the first vibration detector 3, and the second vibration detector 4 are supported by a first frame 9a connected to the above-mentioned support bodies 8a and 8b. The second frame 9b configured to be located at a position symmetrical to the first frame 9a with respect to the longitudinal center axis 1a of the piping 1 is also connected to the support bodies 8a and 8b. The exciter 2 is located at the center of the first frame 9a at an equal distance from the left support body 8a and the right support body 8b, and the first vibration detector 3 and the second vibration detector 4 are located on the first frame 9a at symmetrical positions centered on the exciter 2.

[0085] The excitation circuit 5 excites the vibrator 2 to vibrate the vibration plate provided in the flow path inside the pipe 1. At this time, the fluid in contact with the vibration plate also vibrates together with the vibration plate as an additional mass. Therefore, the vibration plate is excited by the excitation circuit 5 and the vibrator 2 at the primary bending natural vibration frequency in which the additional mass of the fluid is also added, so that the output signals of the first vibration detector 3 and the second vibration detector 4 are always at the maximum.

[0086] As a result, in the absence of fluid flow, the vibration plate vibrates in a primary bending natural vibration mode with the center between the two supporting parts as the antinode of the vibration mode, and the vibration waveforms of the two points measured by the first vibration detector 3 and the second vibration detector 4 have the same phase and the same amplitude.

[0087] On the other hand, when there is a flow of fluid, since the additional mass has a moving speed, a Coriolis force acts on the vibration plate, applying vibration that twists the center of the vibration plate, and causing a phase deviation in the vibration waveforms of the first vibration detector 3 and the second vibration detector 4. The phase deviation is measured by the phase difference measuring device 6, and the measurement result is input to the calculation circuit 7, whereby the calculation circuit 7 can calculate the mass flow rate.

[0088] That is, the Coriolis force F applied to the vibration plate is expressed by the following equation using the additional mass m, the angular velocity ω of the vibration, and the moving velocity V of the fluid.

[0089] [F]=-2m[ω]・[V]

[0090] The above-mentioned additional mass m is a function of the fluid density, the plane size of the vibration plate, and the natural vibration mode. In an actual metering system, it can be expressed as a function of density based on experimental constants related to a fluid with a known density. In addition, since the output signals of the first vibration detector 3 and the second vibration detector 4 are fed back to the excitation circuit 5, and the frequency is scanned in a manner that the vibration amplitude is always maximized, the density of the unknown fluid can be obtained based on the measurement result of the absolute value of the primary natural vibration frequency. Therefore, the density and mass flow rate of the fluid to be measured can be obtained at the same time.

[0091] As described above, a special vibration plate that withstands the Coriolis force from the fluid is arranged in the axial direction inside the pipe 1, and the vibration plate is supported at two points corresponding to the nodes of the primary natural vibration mode in the free state, and is excited at the primary bending natural vibration frequency. At the same time, the vibration waveform is detected by the first vibration detector 3 and the second vibration detector 4 arranged between the two supporting points, and the mass flow rate is calculated based on the phase deviation. Therefore, there is no need to vibrate the entire pipe, and a small mass flow meter with excellent responsiveness can be realized.

[0092] In addition, the vibration plate is excited by a magnetic body such as a permanent magnet fixed on the vibration plate and an exciter 2 arranged outside the piping 1. The vibration plate has a mass distribution such that the first moment relative to the support point is zero, including the mass of the magnetic body fixed to the vibration plate. Therefore, the first natural vibration is not excited by the vibration of the support point, and a mass flow meter that is not easily affected by external vibration can be realized.

[0093] An important feature of the present invention is that "when the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, and the mass of the exciter is set to m3, m3 is greater than the sum of m1 and m2; when the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, the mass of the exciter is set to m3, the sum of m1, m2 and m3 is set to m, the mass of the piping is set to Mt, the mass of the fluid in the piping is set to Mf, and M=Mt+m+Mf, m=0.4M or less", therefore, this feature is described below.

[0094] like Fig.12 As shown in (a) and (b), the phase difference time Δφ between the two sinusoidal waves output by the vibration detector with mass m1 and the vibration detector with mass m2 is proportional to the mass flow rate of the fluid flowing at a flow velocity v in the piping 1a. The above-mentioned two vibration detectors are arranged in a symmetrical position relative to the exciter with mass m3 set in the center of the piping 1a for measuring the flow of fluid in the Coriolis mass flowmeter.

[0095] The Coriolis frequency ω and the density ρ of the above-mentioned sinusoidal waveform have the following relationship.

[0096] That is, if the length of the pipe 1a is L, the elastic modulus of the pipe 1a is E, the section moment of inertia is I, and the cross-sectional area is A, then:

[0097] ω∝(1 / L 2 )(EI / ρA) 1 / 2 (1).

[0098] Here, if the outer diameter of the pipe 1a is D O , set the inner diameter to D i , then the section inertia moment I is expressed as:

[0099] I∝D O 4 -D i 4 (2),

[0100] It is only a function of the size of the pipe 1a.

[0101] In addition, the denominator ρA of the above formula (1) is the total mass per unit length of the pipe 1a. Therefore, if the density of the pipe 1a is ρt and the density of the fluid flowing in the pipe 1a is ρf, the mass per unit length of the pipe 1a, mt, is “ρt×π×(1 / 4)(D O 2 -D i 2 )”, the mass per unit length of the fluid mf is “ρf×π×(1 / 4)(D i 2 )”,ρA can be replaced by “mt+mf”.

[0102] Therefore, if the shape and size of the pipe 1a are the same and the same fluid flows through it, the Coriolis frequency ω is a function that depends only on the elastic modulus E and density ρt of the material of the pipe 1a. Therefore, if the shape and size of the pipe 1a are the same as a premise, the mass of the pipe 1a is set to Mt, and the mass of the fluid in the pipe 1a is set to Mf, then mt and mf can be replaced by Mt and Mf, respectively. In addition, since the additional mass such as the mass m1 and m2 of the vibration detector and the mass m3 of the exciter are added to the pipe 1a independently of the mass Mt of the pipe 1a and the mass Mf of the fluid, the total mass M of the pipe 1a can be expressed as M=Mt+m+Mf.

[0103] Therefore, the above formula (1) can be expressed by the following formula (3):

[0104] ω∝(EI / M) 1 / 2 (3).

[0105] If the shape, size and material of the piping 1a are the same, then in the total mass M (Mt+m+Mf) of the piping 1a, the variable is the mass Mf of the fluid, and Mf is a function of the density ρf. Therefore, according to the above formula (3), the Coriolis frequency ω is estimated as a function of the density ρf. In other words, the small amount Δω of the estimated Coriolis frequency ω is a function of the small amount △ρf of the fluid density. Generally, the sensitivity (frequency change) of a Coriolis mass flowmeter (also a density meter) to changes in fluid density is called the frequency-density margin (Hz / (g / cm 3 The change in fluid density (a tiny amount △ρf) can also be called the measurement resolution of fluid density, and the change in Coriolis frequency ω (a tiny amount △ω) can also be called the measurement resolution of Coriolis frequency. Therefore, it can be said that the frequency density margin (Hz / (g / cm 3 )) Estimate the fluid density measurement sensitivity.

[0106] When the fluid is a gas, it is a compressible fluid, so the pressure and temperature must be fixed for comparison. If we consider the normal case of 1 atmosphere and 0°C, the density of hydrogen is 0.0898 (g / L) and the density of helium is 0.1769 (g / L). The density difference between the two is 0.0871 (g / L), and sensitivity that can detect this density difference is required.

[0107] Here, from Fig.12 A conventional method for detecting the phase difference time Δφ and the Coriolis frequency ω of two sinusoidal waveforms output by two vibration detectors shown in (c) is described. Figure 1 In the embodiment, the output signals from the first vibration detector 3 and the second vibration detector 4 are input to the phase difference measuring device 6. The phase difference measuring device 6 is composed of a preamplifier and an analog-to-digital conversion circuit. After being converted into a digital signal in the phase difference measuring device 6, the calculation circuit 7 performs software calculation, and the phase difference time Δφ and the Coriolis frequency ω can be calculated by calculation. Therefore, usually, the detection resolution of the phase difference time Δφ and the Coriolis frequency ω is restricted by the analog-to-digital conversion resolution of the phase difference measuring device 6 and the fast Fourier transform resolution of the calculation circuit 7.

[0108] Generally, the Coriolis frequency ω, which is determined by the shape and size of the pipe through which the measured fluid flows, is about 100 Hz to 1 kHz. For this frequency band, the analog-to-digital conversion resolution of the normal phase difference measuring device 6 and the fast Fourier transform resolution bandwidth of the calculation circuit 7 of a moderately priced device are about 1 mHz. When the frequency resolution is set to 1 mHz based on the above estimation, if the fluid density measurement resolution Δρ = 0.0871 (g / L) = 0.0871 (mg / cm 3 ) and the Coriolis frequency measurement resolution Δω=1mHz, which is equivalent to Δω / Δρ=1(mHz) / 0.0871(mg / cm 3 )=11.5(Hz / (g / cm 3 )). If the margin is estimated as 4 to 5 times the Coriolis frequency measurement resolution as the measurement accuracy, the frequency density margin is 46~58Hz / (g / cm 3 ).

[0109] When the mass of the first vibration detector is m1, the mass of the second vibration detector is m2, the mass of the exciter is m3, the mass of the pipe is Mt, and the mass of the fluid in the pipe is Mf, Fig.13The horizontal axis is the ratio of the additional mass m (m1+m2+m3) to the total mass M (Mt+m+Mf) of the pipe when the pipe material is CFRTP (symbol "●"), SUS316 (symbol "▲") or PFA (symbol "■"), and the frequency density margin (Hz / (g / cm 3 )) is the vertical axis of the graph, indicating the case where m3 = m1 + m2, Fig.14 The horizontal axis is the ratio of the additional mass m (m1+m2+m3) to the mass M (Mt+m+Mf) of the entire pipe when the pipe material is CFRTP, and the frequency density margin (Hz / (g / cm 3 )) is the graph with the vertical axis. When the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, and the mass of the exciter is set to m3, the symbols "■", "▲", and "●" respectively represent the cases where the ratio of m3 / (m1+m2) is 3 / 1, 2 / 1, and 1 / 1.

[0110] Will Fig.13 and Fig.14 The density of CFRTP (carbon fiber reinforced fluororesin), PFA, and SUS316 used in 3 )、Elastic modulus(GPa)、Linear expansion coefficient(10 -6 / °C) are shown in Table 1 below. Fig.13 and Fig.14 In the calculation, the shape, size, and installation positions of the exciter and vibration detector of the piping other than the material of the piping are all the same. Since the purpose is to measure a small flow rate, the outer diameter and inner diameter of the piping used for the calculation are 1.057 mm and 0.794 mm, respectively. Therefore, since the mass of the piping is small, it can be said that increasing the ratio of the additional mass m to the total mass M will increase the degree of freedom in design. Usually, the exciter needs to input energy to make the piping vibrate at a resonant frequency, using an electromagnetic coil, etc., but it is bound to have a certain degree of mass. On the other hand, if a passive vibration sensor is used as the vibration detector, an AE sensor or an optical displacement sensor using a piezoelectric element that can be lighter can be used as the additional mass instead of heavy objects such as electromagnetic coils.

[0111] [Table 1]

[0112]

[0113] according to Fig.13, when PFA is used to form the piping, sufficient frequency density margin cannot be obtained. This result is the reason why density measurement is not mentioned in the existing technology of using PFA for piping for measuring fluid flow. In addition, in SUS316, which is usually used as a piping material, in order to obtain a sufficient frequency density margin, it must be designed to be less than m=0.2M. On the other hand, when CFRTP is used for piping materials, if m=0.4M or less, a sufficient frequency density margin can be obtained.

[0114] For the Coriolis frequency ω, if the shape and dimensions (length, outer diameter, inner diameter) of the pipe through which the measured fluid flows are constant, then equation (3) becomes a function of only the elastic modulus E and the total mass M (=Mt+m+Mf) of the pipe, as in equation (4):

[0115] ω∝(E / M) 1 / 2 (4).

[0116] Furthermore, if the density of the fluid is constant, Mf is a constant. In addition, Mt is only a function of the density ρt of the pipe. If the material properties of the pipe are constant, the elastic modulus E and Mt are constants. Therefore, focusing on the denominator, equation (4) can be rewritten as:

[0117] ω∝(Mt+m+Mf) -1 / 2 (5).

[0118] Therefore, from the formula (5), it can be assumed that the offset amount Δω of ω changes depending on the ratio of m / (Mt+m+Mf).

[0119] The additional mass m is the sum of the mass m3 of the exciter and the masses m1 and m2 of the vibration detector, but is usually designed to be m1=m2, so the additional mass m can also be expressed as m=m3+2×m1.

[0120] The exciter is set in the center of the pipe. Fig.12 As in (a), the pipe is excited to vibrate and the fluid flows, thereby Fig.12 As shown in (b), torsional vibration caused by the Coriolis force is generated in the piping with the exciter as the rotation axis center. At this time, the mass m3 of the exciter on the rotation axis of the torsional vibration does not contribute to the rotational inertia of the torsional vibration, and only the mass (m1+m2) of the vibration detector is added to the rotational inertia of the torsional vibration. The rotational inertia added to the torsional vibration causes the torsional vibration frequency to change. This torsional vibration frequency is the Coriolis frequency, and the offset Δω of the Coriolis frequency depends on the proportion of the mass (m1+m2) of the vibration detector in the added mass m. Therefore, when the ratio m / (Mt+m+Mf) is a value, by changing the ratio m3 / (m1+m2), as shown in Fig.14 As shown, the frequency density margin changes.

[0121] according to Fig.14 It can be seen that when the mass of the first vibration detector is m1, the mass of the second vibration detector is m2, and the mass of the exciter is m3, the frequency density margin is set to 46mHz / (g / cm 3 ), the ratio of the additional mass m to the total mass M (=Mt+m+Mf) is set to m=0.4M or less when m3 / (m1+m2)=1, to m=0.6M or less when m3 / (m1+m2)=2, and to m=0.8M or less when m3 / (m1+m2)=3. Fig.14 , when m3 / (m1+m2)=2, in the case of m=0.4M, the frequency density margin is 55Hz / (g / cm 3 ), when m3 / (m1+m2)=3, in the case of m=0.4M, the frequency density margin is 61Hz / (g / cm 3 ). Therefore, by making the ratio of m3 / (m1+m2) greater than 1, the frequency density margin can be improved. (The degree of freedom in designing the exciter and the vibration detector can be increased)

[0122] Fig.151 is a schematic diagram of the second embodiment of the Coriolis mass flowmeter of the present invention including related devices. The second embodiment includes a first differential circuit 121 and a second differential circuit 121a, and includes an electromagnetic drive coil 2a (corresponding to a magnetic body such as a permanent magnet described later) as an exciter, and electrostatic capacitance sensors as a first vibration detector 3a and a second vibration detector 4a on a first frame 9a. The electromagnetic drive coil 2a is located at the center of the first frame 9a at an equal distance from the support body 8a on the left and the support body 8b on the right, and the first vibration detector 3a and the second vibration detector 4a are located at symmetrical positions with the electromagnetic drive coil 2a as the center on the first frame 9a. In addition, electrostatic capacitance sensors as the first vibration detector 3a and the second vibration detector 4a are also supported on the second frame 9b in a manner that they are symmetrically located with respect to the first vibration detector 3a and the second vibration detector 4a supported on the first frame 9a across the longitudinal central axis 1a of the pipe 1. Furthermore, the pipe 1 is provided with a magnetic body 2b such as a permanent magnet as an exciter, a non-magnetic body 2c which is located at a symmetrical position with respect to the longitudinal center axis 1a of the pipe 1 and has the same shape and mass as the magnetic body 2b, and metal thin films 3b and 4b. Thus, if a first differential circuit 121 for obtaining the difference of the output of the first vibration detector 3a which is located at a symmetrical position across the longitudinal center axis 1a of the pipe 1a and a second differential circuit 121a for obtaining the difference of the output of the second vibration detector 4a are provided, there is an effect of removing the same-phase signal of the external vibration or the like by measuring the phase difference between the outputs of the respective operation circuits 121 and 121a.

[0123] Here, when the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, and the mass of the exciter is set to m3, m3 is greater than the sum of m1 and m2, the mass of the first vibration detector 3a supported by the first frame 9a and the mass of the first vibration detector 3a supported by the second frame 9b are both m1 / 2, the mass of the second vibration detector 4a supported by the first frame 9a and the mass of the second vibration detector 4a supported by the second frame 9b are both m2 / 2, and if the mass of the magnetic body 2b and the non-magnetic body 2c are both m3 / 2, the same mass is arranged at a symmetrical position across the longitudinal center axis 1a of the pipe 1, so the same moment of inertia is generated with respect to the longitudinal center axis 1a of the pipe 1. In this way, by making the moment of inertia of the vibration direction of the pipe 1 equivalent, it becomes an axisymmetric vibration, which has the effect of removing the in-phase vibration component by obtaining a differential.

[0124] Fig.161 is a schematic structural diagram of the third embodiment of the Coriolis mass flowmeter of the present invention including related devices. The third embodiment includes a first differential circuit 121 and a second differential circuit 121a, and includes a piezoelectric element 2d as an exciter and acoustic sensors as a first vibration detector 3c and a second vibration detector 4c on a first frame 9a. The piezoelectric element 2d is located at the center of the first frame 9a at an equal distance from the right support body 9a and the left support body 9b, and the first vibration detector 3c and the second vibration detector 4c are located on the first frame 9a at symmetrical positions centered on the piezoelectric element 2d. In addition, acoustic sensors as the first vibration detector 3c and the second vibration detector 4c are also supported on the second frame 9b in a manner that they are located at symmetrical positions relative to the first vibration detector 3c and the second vibration detector 4c supported on the first frame 9a across the longitudinal center axis 1a of the piping 1. In addition, the piping 1 includes an equivalent mass 2e.

[0125] Fig.17 1 is a schematic structural diagram of a fourth embodiment of the Coriolis mass flowmeter of the present invention including related devices. The fourth embodiment includes a first differential circuit 121 and a second differential circuit 121a, and includes an electromagnetic drive coil 2a as an exciter, and optical displacement sensors as a first vibration detector 3d and a second vibration detector 4d on a first frame 9a. The electromagnetic drive coil 2a is located at the center of the first frame 9a at an equal distance from the right support body 9a and the left support body 9b, and the first vibration detector 3d and the second vibration detector 4d are located at symmetrical positions with respect to the electromagnetic drive coil 2a on the first frame 9a. In addition, the optical displacement sensors as the first vibration detector 3d and the second vibration detector 4d are also supported on the second frame 9b in a manner that they are located at symmetrical positions with respect to the first vibration detector 3d and the second vibration detector 4d supported on the first frame 9a across the longitudinal central axis 1a of the pipe 1. Furthermore, the pipe 1 includes a magnetic body 2b as an exciter, a non-magnetic body 2c which is located symmetrically with the magnetic body 2b with respect to the longitudinal center axis 1a of the pipe 1 and has the same shape and mass as the magnetic body 2b, and metal films 3b and 4b.

[0126] Fig.181 is a schematic structural diagram of the fifth embodiment of the Coriolis mass flowmeter of the present invention including related devices. The fifth embodiment includes a first differential circuit 121 and a second differential circuit 121a, and includes an electromagnetic drive coil 2a as an exciter, and acceleration sensors as a first vibration detector 3e and a second vibration detector 4e on a first frame 9a. The electromagnetic drive coil 2a is located at the center of the first frame 9a at an equal distance from the right support body 9a and the left support body 9b, and the first vibration detector 3e and the second vibration detector 4e are located on the first frame 9a at symmetrical positions with the electromagnetic drive coil 2a as the center. In addition, the acceleration sensors as the first vibration detector 3e and the second vibration detector 4e are also supported on the second frame 9b in a manner that they are located at symmetrical positions relative to the first vibration detector 3e and the second vibration detector 4e supported on the first frame 9a across the longitudinal central axis 1a of the pipe 1. Furthermore, the pipe 1 is provided with a magnetic body 2b and a non-magnetic body 2c. The magnetic body 2b serves as an exciter. The non-magnetic body 2c is located symmetrically to the magnetic body 2b relative to the longitudinal center axis 1a of the pipe 1 and has the same shape and mass as the magnetic body 2b.

[0127] Description of Reference Numerals

[0128] 1 piping

[0129] 2, 2a, 2d Vibrator

[0130] 2b Magnetic bodies such as permanent magnets

[0131] 2c Non-magnetic material

[0132] 2e equivalent mass

[0133] 3, 3a, 3c, 3d, 3e First vibration detector

[0134] 3b Metal film

[0135] 4, 4a, 4c, 4d, 4e Second vibration detector

[0136] 4b Metal film

[0137] 5 Excitation circuit

[0138] 6 Phase difference measurement device

[0139] 7 Operational Circuit

[0140] 8a Support body on the right

[0141] 8b Left support

[0142] 9a First Frame

[0143] 9b Second Frame

[0144] 121 First differential circuit

[0145] 121a Second differential circuit

Claims

1. A Coriolis mass flowmeter, characterized in that: The invention comprises: a straight pipe for allowing a measuring fluid to flow; a vibration exciter for exciting the pipe; a first vibration detector and a second vibration detector for detecting the vibration state of the pipe; and a support body for supporting two ends of the pipe so that the two ends of the pipe become fixed ends relative to the vibration. The vibration exciter, the first vibration detector and the second vibration detector are supported by a frame, and the frame is connected to the support body. The mass flow rate of the fluid flowing in the pipe is calculated based on the phase deviation of the vibration waveform detected by the first vibration detector and the second vibration detector. The pipe, the support body and the frame are formed of a highly elastic plastic material.

2. The Coriolis mass flowmeter according to claim 1, wherein: The highly elastic plastic material is carbon fiber reinforced thermoplastic.

3. The Coriolis mass flowmeter according to claim 2, characterized in that The thermoplastic is fluororesin.

4. The flow measurement device according to any one of claims 1 to 3, characterized in that: When the mass of the first vibration detector is m1, the mass of the second vibration detector is m2, and the mass of the exciter is m3, m3 is larger than the sum of m1 and m2.

5. The Coriolis mass flowmeter according to any one of claims 1 to 3, characterized in that: When the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, the mass of the exciter is set to m3, the total of m1, m2 and m3 is set to m, the mass of the piping is set to Mt, the mass of the fluid in the piping is set to Mf, and M=Mt+m+Mf, m=0.4M or less.

6. The Coriolis mass flowmeter according to any one of claims 1 to 3, characterized in that: The first vibration detector and the second vibration detector are acceleration sensors located at symmetrical positions with respect to the vibration exciter.

7. The Coriolis mass flowmeter according to any one of claims 1 to 3, characterized in that: The first vibration detector and the second vibration detector are acoustic sensors located at symmetrical positions with the vibration exciter as the center.

8. The Coriolis mass flowmeter according to any one of claims 1 to 3, characterized in that: The exciter is a piezoelectric element.

9. A Coriolis mass flowmeter, characterized in that: The invention comprises: a straight pipe for flowing a measuring fluid; a vibration exciter for vibrating the pipe; a first vibration detector and a second vibration detector for detecting a vibration state of the pipe; and a left support and a right support for supporting both ends of the pipe so that both ends of the pipe become fixed ends with respect to vibration, the vibration exciter, the first vibration detector and the second vibration detector are supported by a frame, the frame is at least one of a first frame and a second frame connected to the support, the mass flow rate of the fluid flowing in the pipe is obtained based on the phase deviation of the vibration waveform detected by the first vibration detector and the second vibration detector, the pipe is formed by a straight pipe, the first frame and the second frame are located at symmetrical positions with respect to the longitudinal central axis of the pipe, the vibration exciter is located at the center of the first frame equidistant from the left support and the right support, the first vibration detector and the second vibration detector are located on the first frame at symmetrical positions with respect to the vibration exciter as the center, and the first vibration detector and the second vibration detector are also supported on the second frame in a manner that they are located at symmetrical positions with respect to the first vibration detector and the second vibration detector supported on the first frame with respect to the longitudinal central axis of the pipe.

10. The Coriolis mass flowmeter according to claim 9, characterized in that A differential circuit for obtaining a difference in outputs of the first vibration detector and a differential circuit for obtaining a difference in outputs of the second vibration detector are provided, and the in-phase signal is removed by measuring a phase difference between the outputs of the two differential circuits.

11. The Coriolis mass flowmeter according to claim 10, wherein: The first vibration detector and the second vibration detector are electrostatic capacitance sensors, and metal thin films are attached to the pipes.

12. The Coriolis mass flowmeter according to any one of claims 9 to 11, characterized in that: The first vibration detector and the second vibration detector are optical displacement sensors, and a metal thin film is attached to the pipe.

13. The Coriolis mass flowmeter according to any one of claims 9 to 11, characterized in that: The exciter is composed of a magnetic body such as a permanent magnet and an electromagnetic drive coil corresponding to the magnetic body. The above-mentioned magnetic body is an exciter supported on the piping and excites the piping. A non-magnetic body with the same shape and mass as the magnetic body is supported on the piping in a manner that is symmetrical to the above-mentioned magnetic body relative to the central axis in the longitudinal direction of the piping.

14. The Coriolis mass flow meter of claim 13, wherein: When the mass of the first vibration detector is set to m1, the mass of the second vibration detector is set to m2, and the mass of the exciter is set to m3, m3 is greater than the sum of m1 and m2, the mass of the first vibration detector supported by the first frame and the mass of the first vibration detector supported by the second frame are both m1 / 2, the mass of the second vibration detector supported by the first frame and the mass of the second vibration detector supported by the second frame are both m2 / 2, and the mass of the magnetic body and the non-magnetic body are both m3 / 2.

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